#technical question

Star Wars technical question:  How does blockading a hyperspace lane work?  I’m watching this episode of Rebels where they say that the Empire will track any ship that attempts to leave the system. And then Thrawn talks about them “evading our blockade” a few minutes later. Here’s what I’m thinking:  -You can only leave and enter systems through established hyperspace lanes; otherwise you’ll hit something. This makes it possible to blockade a system--you just hang out at the blockade.  -I know the Empire develops a weapon that pulls ships from hyperspace in S2, but I’m not at all clear about how it DETECTS ships in hyperspace, since that never actually seems to happen (or at least we’re not shown a mechanism for it).  -It doesn’t seem like it would be too hard to blockade a hyperspace lane, whether you know a ship is using it or not--just throw literally any object into it and any ship travelling through hyperspace will hit it and be destroyed. I think.  -But how do you TRACK a ship leaving the system? To what extent can a ship’s place be known at any given moment if it’s in hyperspace?  What do you know about this, tumblr? Help me out. 

Another Star Wars technical question:  A ship can dock with another ship and take it through hyperspace, but what are the size limits on that? Does it matter?  For instance, a small TIE fighter can dock on the belly of a Star Destroyer and they take off through hyperspace, no problem. What if the fighter was the one with the hyperdrive and the Star Destroyer the one tagging along? Would that work? What’s the mechanism, here?